1. Field
This disclosure is directed to a multilayer film, a method for producing the multilayer film, and an article including the multilayer film. In particular, it is related to an encapsulating structure that includes the multilayer film.
2. Description of the Related Art
With recent rapid advances in electronics technology, articles such as flat panel displays, including liquid crystal displays, plasma displays, electroluminescence (EL) displays and light-emitting diodes are seeing widespread commercial use. Particularly, EL displays have drawn considerable attention due to their advantages of high luminescence efficiency, wide viewing angle and rapid response speed.
A typical organic EL device of an EL display has a structure in which an organic multilayer film that includes a light-emitting layer, a hole injecting layer and an electron injecting layer is interposed between a pair of electrodes on a substrate. The organic EL device utilizes a phenomenon in which electrons injected from the electron injecting layer recombine with holes injected from the hole injecting layer in the light-emitting layer to emit light.
The light-emitting layer of the organic EL device is composed of an organic fluorescent material. High sensitivity of the organic fluorescent material to environmental factors, such as moisture and oxygen, may make the metal electrodes (which are formed directly on the light-emitting layer or separately from the light-emitting layer by the hole injecting layer/electron injecting layer), susceptible to oxidation, resulting in a rapid deterioration in the luminescent properties of the organic EL device when being driven under ambient conditions. Thus, encapsulation of the organic EL device is used to protect the EL device from attack by moisture, oxygen, and the like, and to extend the lifetime of the EL device.
A general thin-film encapsulation material for an organic EL device contains alternating polymer layers and inorganic barrier layers. The inorganic barrier layers serve to prevent moisture and gases from entering the EL device, while the polymer layers serve as buffers to relieve internal stress of the inorganic barrier layers or fill fine cracks or pin holes present in the inorganic barrier layers.
The polymer layers are mainly formed by depositing an acrylic or epoxy monomer under vacuum and curing the monomer by UV or E-beam irradiation or plasma-polymerizing the monomer under vacuum. Alternatively, the polymer layers are formed by coating a monomer (in its liquid state) via spin coating or casting at atmospheric pressure and irradiating the coating with UV light to cure the monomer. The inorganic barrier layers can be formed using a variety of materials (e.g., metals, metal oxides and metal nitrides) with good gas and moisture barrier properties by processes, such as, for example, sputtering, chemical vapor deposition and E-beam deposition.
In the formation of the polymer layers, after the monomer is directly deposited on a substrate under vacuum, the monomer is in a liquid state prior to curing. This causes the monomer to be adsorbed on the surface of the organic EL device or to be diffused into the device, resulting in a deterioration in the characteristics of the device.
Further, UV irradiation for curing the monomer may bring about additional deterioration in the characteristics of the organic EL device and its principal constituent organic materials. In particular, when a polymer layer formed in direct contact with the organic EL device it may fatally impair the characteristics of the organic EL device.
The organic EL device is directly exposed to plasma during plasma polymerization for the formation of the polymer layers. This exposure may degrade the organic materials or make the structure of the device unstable, which has a direct influence on the characteristics of the organic EL device.
Most processes for the formation of the inorganic barrier layers employ a variety of plasma sources depending on the processing conditions, thus making it difficult to form the inorganic barrier layer in direct contact with the organic EL device. In conclusion, it is desirable to develop a suitable process for the formation of the organic polymer layer that is in direct contact with the organic EL device. A suitable process that can be used to dispose an organic polymer layer in contact with the organic EL device can improve the characteristics of the device.